The present invention relates to a segment-type liquid crystal display panel suitable for displaying information by numerals and alphabets, for example, time information or calendar of a timepiece, or a telephone number of a cellular phone (portable telephone).
There are segment-type and matrix-type liquid crystal display panels for digital display, each for displaying information by characters and numerals. The segment type is positively used as a display portion of a timepiece, a cellular phone, or the like because of ease for use and low manufacturing cost though it has low flexibility of display (display capacity) as compared to the matrix type.
A conventional segment-type liquid crystal display panel is structured such that two glass substrates have a liquid crystal layer sandwiched therebetween, one of the substrates has thereon a plurality of segment electrodes of segment-type electrodes forming a pattern of numeral or the like, and the other substrate has thereon an opposite electrode which is disposed to face the segment electrodes to perform a display by a pattern of combination of the segment electrodes through use of optical change in the liquid crystal layer caused by selectively applying voltage to the liquid crystal layer by means of the segment electrodes and the opposite electrode.
Hence, in such a conventional segment-type liquid crystal display panel, only a portion where the segment electrode and the opposite electrode overlap each other operates as a pixel area (display area), but a display state in the other area (background area) can not be controlled.
Accordingly, specifically in the case in which a mixed liquid crystal layer composed of a liquid crystal and a transparent solid substance is used as the liquid crystal layer, and when the liquid crystal layer has a scattering property where no voltage is applied thereto or when it has a transmission property where no voltage is applied thereto, it is impossible to easily reverse brightness and darkness of the display as in the liquid crystal display panel using a twisted nematic liquid crystal layer or the like and a polarizer.
Similarly, also when a mixed liquid crystal layer composed of a liquid crystal and a dichroic dye is used as the liquid crystal layer, it is impossible to easily reverse a transmission area and a colored area in the liquid crystal layer.
In the case of the liquid crystal display panel using a twisted nematic (TN) liquid crystal layer or a super twisted nematic (STN) liquid crystal layer and a polarizer, brightness and darkness of display can be reversed by an attaching angle of the polarizer but it is impossible to perform a display by optionally controlling brightness and darkness of the display area and the background area.
One example of the conventional segment-type liquid crystal display panel is now explained with reference to the drawings. FIG. 34 is a plane view showing an enlarged arrangement example of segment electrodes and an opposite electrode in the conventional segment-type liquid crystal display panel, and FIG. 35 is a partially enlarged cross-sectional view of the liquid crystal display panel taken along a line XXXVxe2x80x94XXXV in FIG. 34.
In this liquid crystal display panel, as shown in FIG. 35, a first substrate 1 that is a transparent glass substrate disposed at the upper side (visible side) and a second substrate 2 that is a transparent glass substrate disposed at the lower side (the opposite side to the visible side) are coupled together with a predetermined gap intervening therebetween with spacers and a sealing material which are not shown, and a liquid crystal layer 3 is sealed in the gap, which is composed of a mixed liquid crystal of a liquid crystal and a transparent solid substance.
On the first substrate 1 (inner surface), as clearly shown in FIG. 34, a plurality of segment electrodes 5a to 5g (referred to as xe2x80x9csegment electrodes 5xe2x80x3 when they are collectively called) are provided, which are made of a transparent conductive film. On the other hand, on the second substrate 2 (inner surface), an opposite electrode 6 made of a transparent conductive film is provided to face the entire region including the segment electrodes 5a to 5g. 
In this example, seven segment electrodes 5a to 5g take a pattern arrangement of the form of xe2x80x9c8xe2x80x9d, and gaps are provided between the segment electrodes 5a to 5g respectively. This is a so-called seven-segment type arrangement. Further, the segment electrodes 5a to 5g have respective wiring electrodes 12 which are respectively connected to segment electrode terminals (not shown) for individually applying external signals thereto.
Overlaps between the segment electrodes 5a to 5g and the opposite, electrode 6 form a pixel area (display area) 32, and the other portion forms a background area 33.
The transparent solid substance in the liquid crystal layer 3 is formed in such a manner that a liquid crystal, in which an organic monomer is dissolved in advance, is injected into the gap between the first substrate 1 and the second substrate 2 and then applied with ultraviolet light.
A display by this liquid crystal display panel is performed utilizing anisotropy of optical refractive index of the mixed liquid crystal forming the liquid crystal layer 3. More specifically, when optical refractive indices of the liquid crystal and the transparent solid substance which constitute the mixed liquid crystal are substantially the same, the display becomes transparent, and as both optical refractive indices become different, its scattering degree increases.
Actually, a predetermined signal (voltage) is selectively applied to the liquid crystal layer 3 by the segment electrodes 5 and the opposite electrode 6 which are in contact with both upper and lower surfaces of the liquid crystal layer 3 respectively to control the optical refractive index of the mixed liquid crystal, thereby performing a desired display.
For example, when numeral xe2x80x9c1xe2x80x9d is displayed, voltage is applied between the segment electrodes 5c and 5g, and the opposite electrode 6, and not applied between the other segment electrodes 5a, 5b, 5d, 5e and 5f, and the opposite electrode 6, whereby only portions of the pixel area 32 where the liquid crystal layer 3 is sandwiched between the segment electrodes 5c and 5g, and the opposite electrode 6 reduce in scattering degree (increase in transmittance) to have a scattering degree different from that of the other portion of the pixel area 32 and background area 33, thereby enabling recognition of xe2x80x9c1xe2x80x9d.
In such a conventional liquid crystal display panel, however, scattering and transmission of the liquid crystal layer 3 at the pixel area 32 provided with the segment electrodes 5 can be controlled by applying voltage between the segment electrodes 5 and the opposite electrode 6, but they at the background area 33 around the pixel area 32 can not be controlled, allowing the liquid crystal layer 3 at the background area 33 to always maintain the scattering state.
Accordingly, in order to bring the background area 33 into the transmission state, it is necessary to improve the material of the mixed liquid crystal or manufacturing method. It is impossible to easily reverse the brightness and darkness of the display by changing the attaching angle of the polarizer as in the conventional liquid crystal display panel by way of combination of the twisted nematic (TN) liquid crystal layer or the super twisted nematic (STN) liquid crystal layer and the polarizer.
Further, when the above-described mixed liquid crystal layer is used, it is impossible to optionally perform in the same liquid crystal display panel, for example, a display in which the background area 33 is in a scattering state and the pixel area 32 is in a transmission state and a display in which conversely the background area 33 is in a transmission state and the pixel area 32 is in a scattering state.
Furthermore, even when the twisted nematic (TN) liquid crystal layer or the super twisted nematic (STN) liquid crystal layer and the polarizer are used, it is impossible to electrically reverse bright and dark states of the pixel area and the background area when necessary in the same liquid crystal display panel.
This is the same also in a liquid crystal display panel using a mixed liquid crystal layer containing a liquid crystal and a dichroic dye as a liquid crystal layer.
Therefore, it is desired to control the quantity of transmission, scattering or absorption of light at the background area and the pixel area in the liquid crystal display panel for performing a display by change in the quantity of transmission, scattering or absorption of light by the liquid crystal layer without changing material and manufacturing method of the liquid crystal layer.
Moreover, it is difficult in the conventional liquid crystal display panel to allow an observer to recognize information behind the liquid crystal display panel by controlling the quantity of transmission, scattering or absorption of light at the background area, or to dispose a photovoltaic device such as a solar cell behind the liquid crystal display panel and apply required light thereto.
The invention is made in view of the above-described technical background, and its object is to make it possible to optionally reverse brightness and darkness of the pixel area and the background area of a liquid crystal display panel for displaying various kinds of information, to optionally control the quantity of transmission, scattering or absorption of light in the background area, allowing information behind the liquid crystal display panel to be viewed, or to dispose a photovoltaic device therein and optionally control the quantity of its power generation, thereby improving variety of visual design and function of a device using the liquid crystal display panel.
In order to achieve the above-described object, a liquid crystal display panel, which includes a liquid crystal layer sandwiched between transparent first and second substrates, and a plurality of segment electrodes on the first substrate and an opposite electrode on the second substrate respectively to perform a display by a change in a state of transmission, scattering or absorption of light which is made incident on the liquid crystal layer, caused by selectively applying voltage to the liquid crystal layer by means of the segment electrodes and the opposite electrode, is structured as follows.
Specifically, an auxiliary electrode is provided around each segment electrode on the first substrate with a slight gap intervening between the segment electrode and the auxiliary electrode, and the auxiliary electrode is formed of the same transparent conductive film as that of the segment electrodes, and an overlap between the opposite electrode and the segment electrode forms a pixel area, and an overlap between the opposite electrode and the auxiliary electrode forms a background area.
Further, it is preferable to provide a plurality of segment electrode terminals for individually applying external signals to the plurality of segment electrodes, and wiring electrodes for connecting the segment electrode terminals and the segment electrodes respectively, in which the auxiliary electrode is provided with a slight gap intervening also between the auxiliary electrode and the wiring electrode, the auxiliary electrode, the segment electrodes and the wiring electrodes are formed of the same transparent conductive film, and overlaps between the opposite electrode and the wiring electrodes also form the background area.
It is desirable to make the gap between the wiring electrode and the auxiliary electrode on the first substrate smaller than the gap between the segment electrode and the auxiliary electrode.
It is desirable that at least a portion of the wiring electrode with a gap formed between the wiring electrode and the auxiliary electrode is made a thin wire electrode portion having a width that is the same as or smaller than that of the gap.
It is preferable that the wiring electrode outside an outer periphery of the background area is a thick wire electrode portion having a width larger than that of the thin wire electrode portion.
In this case, it is preferable to protrude a portion of an outer peripheral portion of the auxiliary electrode close to the thin wire electrode portion to be close to the thick wire electrode portion of the wiring electrode to form a gap between the protruding portion and the thick wire electrode portion, which is smaller than a gap between the protruding portion and the thin wire electrode portion.
It is desirable that the thick wire electrode portion of the wiring electrode has a connection side portion for connecting the thin wire electrode portion and the segment electrode terminal, and an extending portion extending to the opposite side to the portion, and a gap between the protruding portion of the auxiliary electrode and the extending portion of the wiring electrode is smaller than a gap between the protruding portion of the auxiliary electrode and the connection side portion.
Alternatively, it is also suitable to provide an auxiliary electrode made of a transparent conductive film between each segment electrode and around the segment electrodes on the first substrate to overlap peripheral portions of the segment electrodes, and to electrically insulate the auxiliary electrode from each segment electrode by a transparent insulating film which is provided between the auxiliary electrode and the segment electrode.
In this case, it is preferable to form each segment electrode directly on the first substrate, the insulating film on the first substrate and at least on a peripheral portion of each segment electrode, and the auxiliary electrode on the insulating film.
It is suitable to form the auxiliary electrode and the insulating film in the same planar pattern.
Alternatively, it is also suitable to form the auxiliary electrode directly on the first substrate, the insulating film on the first substrate within opening portions in the auxiliary electrode and at least on peripheral portions of the opening portions in the auxiliary electrode, and the segment electrodes on the insulating film.
In this case, it is suitable to form the segment electrode and the insulating film in the same planar pattern.
Alternatively, it is also suitable to provide an auxiliary electrode made of a transparent conductive film over the entire region forming pixel areas and a background area on the first substrate, a transparent insulating film on An the auxiliary electrode, and each segment electrode on the insulating film, thus an overlap between the opposite electrode and the segment electrode forms the pixel area, and an overlap between the opposite electrode and a portion of the auxiliary electrode without the segment electrodes forms the background area.
In this case, the insulating film on the auxiliary electrode may be removed at portions where the segment electrodes are not provided.
Furthermore, it is also possible to provide a plurality of segment electrode terminals for individually applying external signals to the plurality of segment electrodes, and wiring electrodes for connecting the segment electrode terminals and the segment electrodes respectively on the first substrate, and to extend one end portion of each wiring electrode to a segment electrode forming region, wherein a transparent insulating film is provided on the first substrate and each wiring electrode, and the insulating film has an opening portion on the one end portion of each wiring electrode, and each segment electrode and the auxiliary electrode are provided on the insulating film, and each segment electrode and each wiring electrode are connected through the opening portion of the insulating film.
A photovoltaic device may be disposed outside the second substrate of the liquid crystal display panel. Furthermore, a plurality of holes may be formed in the wiring electrode.
When the segment electrodes and wiring electrodes are formed of a metal plate, sufficient electrical conduction can be obtained even if the wiring electrodes are formed extremely thin to be negligible. However, in this case, the first substrate formed thereon with the segment electrodes is disposed on the opposite side to the visible side.
The auxiliary electrode or the opposite electrode may be formed split into a plurality of parts. When the opposite electrode is formed split into a plurality of parts, gaps between the split opposite electrodes and gaps between the plurality of segment electrodes are preferably provided at different positions in a plane view.
In the liquid crystal display panel according to the invention, since the auxiliary electrode is arranged around the segment electrodes, and the opposite electrode is also disposed on the region facing the auxiliary electrode to constitute the background area as described above, it is possible to apply voltage even to the background area where the opposite electrode and the auxiliary electrode face each other through the liquid crystal layer as in the pixel area where the segment electrode and the opposite electrode face each other even through the same liquid crystal layer as the conventional one is used, thereby changing the display at the background area in the same manner as that at the pixel area.
Further, the auxiliary electrode is formed of the same transparent conductive film as that of the segment electrode with a predetermined gap provided between the auxiliary electrode and each segment electrode, whereby the auxiliary electrode can be formed using the conventional segment electrode pattern forming step, which makes it possible to obtain the segment-type liquid crystal display panel capable of various types of displays with little burden on the step.
Further, the width of the wiring electrode which is connected to each segment electrode to apply a predetermined voltage from an external circuit to each segment electrode is made small, thereby decreasing an optical change in the liquid crystal layer between the wiring electrode and the opposite electrode which influences the display at the background area.
Hence, for example, the segment electrode gap between the segment electrode and the auxiliary electrode and the wiring gap between the wiring electrode and the auxiliary electrode are made 30 xcexcm or smaller, thereby allowing the background area to perform a display with receiving little influence of the wiring electrode.
Further, the provision of the insulating film between the segment electrode and the auxiliary electrode and between the wiring electrode and the auxiliary electrode makes it possible to overlap the segment electrode and the auxiliary electrode, or the wiring electrode and the auxiliary electrode, thereby further decreasing influence of the wiring electrode on the background area.
The insulating film is provided on the segment electrodes and the surroundings and the wiring electrodes, and the auxiliary electrode is provided on the insulating film, thereby eliminating influence of the wiring electrodes and further eliminating the segment electrode gap between the background area and the pixel area to achieve an excellent display quality.
Further, the wiring electrodes are provided on the upper substrate, the segment electrodes are provided through the insulating film, each wiring electrode and each segment electrode are electrically connected to each other through the opening portion which is provided at a part of the insulating film, each segment electrode is electrically isolated, and further the auxiliary electrode is provided around the segment electrode with a predetermined gap intervening therebetween, thereby making it possible to perform a substantially entirely uniform display even in the case of a complex wiring electrode. This is effective especially when the display of the liquid crystal display panel is enlarged for use.
Furthermore, the auxiliary electrode which is provided around the segment electrodes is split into a plurality of parts, thereby making it possible to conduct a control splitting the display state at the background area into a plurality of parts by controlling voltage between the opposite electrode and each of the split auxiliary electrodes.
Further, a shielding layer or a printing layer is provided between the auxiliary electrodes split in a plurality of parts, thereby improving visibility of a display of each auxiliary electrode.
Further, in the segment-type liquid crystal display panel having segment electrodes, a plurality of which are connected to each other, and opposite electrodes separated corresponding to the connected segment electrodes, additional opposite electrodes are provided with slight gaps between the additional electrodes and the split opposite electrodes, and signals are applied to the additional opposite electrodes and the auxiliary electrodes, thereby achieving an entirely uniform display.